Method of making getter material



Patented, Nov. 6, 1934 1,979,506 thereon or MAKING GETTER MATERIAL Stanton Umbreit, West Orange, N. 3., assignor to Radio Corporation of America, a corporation oi Delaware No Drawing. Application September 1, 1932, o Serial No. 631,366

3 Claims.

The invention relates generally to the production of high vacua in thermionic tube devices, and more particularly to a method of making getter material capable of efiiciently removing or absorbing gases remaining after the tube is taken off the pump and sealed.

It is an object of the present invention to provide a getter material which is relatively stable in air,'brittle enough for grinding into powder and compressing into pellets, and ductile enough to remain as a pellet, that is, having sufiicient cohesion for sticking together after being formed.

Another object of the invention is to provide a getter material which, after grinding, may be combined with a nitrocellulose .binder' and used in paste form and painted on to the getter tab.

Other objects and advantages will be made apparent by the following description.

It has been known in the prior art to efiect the final clean-up of the residual gases in vacuum tubes by the use of magnesium, magnesium-barium, or barium alone. Magnesium as a getter material is objectionable in that it does not absorb nitrogen, and that the vaporization takes place so suddenly'and at such a low temperature that the clean-up may be incomplete. When the magnesium is alloyed with other materials, such as barium, the early vaporization of the magnesium confuses the determination of the barium vaporization. It is therefore desirable that magnesium be eliminated as a constituent of the getter material. Barium alone is unstable in air and gives some dificulty in this respect even when enclosedv in copper tubing. In addition, it is difficult to obtain sufficient heat to vaporize the barium when it is enclosed in the copper tubing.

A barium-aluminum composition or alloy is desirable in that the barium is vaporized leaving the aluminum behind; the clean-up action being due to barium alone. It is of course possible, if a tungsten or molybdenum tab is used, to vaporize the aluminum. This may be desirable with transmitting tubes, but it is a costly and needless operation with receiving tubes.

I have found a 50-50 composition or alloy of barium-aluminum, which is quite stable in air, a highly efficient getter. Less than 40% of barium produces an alloy which is not suificiently stable in moist air and is too ductile for proper 5o grinding. More than 60% produces an alloy too unstable to use satisfactorily, if it is desired to keep the getter any length of time. If more than this amount of barium is used, special conditions must be observed-the getter should be used before it has an opportunity to oxidize to an appregiven below for comparison:

760 mm. 1 micron The barium aluminum alloy is prepared by fusion in a high frequency furnace, in an atmosphere of helium, or other inert gas. In the preparation of this alloy by the usual method, there is a large liberation of heat and gas causing foaming or priming which may be so severe as to eject some of the metal from the crucible. The foamso ing may be reduced by melting one constituent and adding successively small amounts of the other.

In practice I have been using in the laboratory 2. 50 cc. iron crucible and melting therein 50 35 grams of aluminum in an atmosphere of helium, argon, etc. The melting is conveniently carried out with theaid of the high frequency furnace. After the aluminum is melted it is allowed just to freeze and one-third of the barium introduced. The crucible is again heated to fusion of the'mixture, which is then re-frozen and another third of barium added. This is again melted and frozen and the final third, that is, the remainder, of the 50 grams of barium added. In this way there as is no ejection of the material or too sudden an evolution of gas. The high frequency heatingives fine stirring and thoroughly mixes the materials. v I

After the mixture is completed, it is allowed to 0001 and then it is chipped out of the crucible; this is easily done. Pieces are then ground to the desired fineness and the material formed into pellets. If desired, the mixture when ground may be combined with a suitable binder, nitrocellulose for example, and used in paste form by painting on to thegetter tab.

When used as a pellet, it should be placed close the edge Qf the getter tab in order that it may 1% more readily be heated by the high frequency currents employed to flash the getter.

If it is desirable to use the material in wire form, an alloy containing approximately 25% barium is satisfactory. This material in wire form is sufiiciently stable for practical use.

What I claim is:

1. The method of preparing getter material containing substantially equal amounts of barium and aluminum, which consists in melting the aluminum in an atmosphere of an inert gas, allowing the melt to freeze, adding a portion of the barium thereto, reheating to the fusion temperature and allowing the melt to refreeze, and repeating the'processuntil all of the barium has been added and fused with the aluminum.

2. The method of preparing .g'etter .material containing an alkaline earth metal and aluminum, which consists in melting one of the metals and then in succession adding a fraction of the required amount of the other metal, solidifying the melted mixture, adding another fraction of STANTON UNIBREIT. 

